Continuous-flow systems heat water on demand — never run out, smaller footprint, lower running costs than storage equivalents.
Instantaneous, or continuous-flow, hot water systems heat water only as it flows through the unit, so you never run out and there is no tank losing heat overnight. AHHAC sizes Rinnai Infinity and Rheem continuous-flow units to your peak demand, typically 16 litres per minute for one bathroom, 20 for two and 26 for three or more, and installs them across Sydney, Melbourne and Brisbane. With regular servicing, expect a unit life of 20+ years.
Reviewed by the AHHAC Technical Team — licensed plumbers & hydronic engineers, NSW Lic 262528C.How we write & review
Instantaneous (or 'continuous-flow') gas systems heat water as it flows through a finned heat exchanger — only when you need it. They're the dominant choice for new Australian homes for good reason.
We install Rinnai Infinity and Rheem Continuous-Flow ranges, sized to your peak flow requirement (number of bathrooms, fixtures running simultaneously).
Instantaneous hot water systems rarely fail to deliver, but they behave differently from a tank, and most of the questions we get come from not knowing what to expect. These are the four we hear most, and how we design around them.
Sizing is about how many outlets run at once, not how many people live in the home. We start from the bathroom count, then adjust for baths, spa fills and the dishwasher or laundry running during morning showers. If you sit between two sizes, going up one step costs less than living with a unit that drops temperature every time someone turns on the kitchen tap.
Gas is the usual fuel. Electric continuous-flow exists, but a whole-house electric unit draws a very large current and often needs three-phase power, so it suits small apartments or single outlets better. A continuous-flow gas unit can also boost rooftop solar collectors, explained in our solar hot water and heat pump guide. For gas supply and flue requirements, see gas hot water systems, and for the Infinity range, our Rinnai hot water page.
Written from on-site experience by the AHHAC Technical Team.
AHHAC's in-house design and service team — licensed plumbers and hydronic engineers (Lic 262528C) who have designed and installed 2,400+ hydronic heating, cooling and hot water systems across Australia since 1998.
Every plumbing and hot water job is assessed on site, carried out by our own licensed plumbers and gasfitters to AS/NZS 3500 (plumbing) and AS/NZS 5601 (gas), pressure-tested and documented, and backed by ongoing service. Nothing is subcontracted out.
Almost never. Continuous-flow systems heat water on demand — every Rinnai Infinity model is rated for 6+ outlets running simultaneously with stable temperature. Practical answer: even a large family running multiple showers + dishwasher + laundry at once has zero issue.
20+ years with annual servicing. The Rinnai Infinity range carries a 12-year heat exchanger warranty — industry-leading. Modern continuous-flow systems easily outlast traditional storage tanks.
Yes — most Rinnai and Rheem continuous-flow units have a pre-heat option that keeps the heat exchanger warm, delivering hot water within 2–3 seconds of opening the tap. Optional add-on, slightly higher running cost.
"AHHAC delivered our 22-zone underfloor system on time, on budget and to spec. The crew were tidy, the documentation was thorough, and the commissioning was textbook."
"We've worked with AHHAC for 17 years. They've installed and serviced our hot water plant across three commercial buildings — and they pick up the phone on weekends."
"Three mobs quoted us; AHHAC's design was the only one based on a proper heat-loss calculation. The system runs beautifully — the others would've been oversized and expensive."